Hi @acesontop. I also wandered about this awhile ago and looked it up. A Plankton is the lowest ranking on Steemit and what most of us started on day one with unless we invested and powered up.
A Plankton is 0-500 SP and hold less than 1 Million Vests
A Minnow is more than 500 SP and less that 4999 SP and hold less than 10 Million vests
A Dolphin is more than 5000 SP and less than 49 999 SP and hold less than 100 Million vests
An Orca is more than 50 000 SP and less than 500 000 SP and hold less than 1000 Million vests
A Whale is 500 000 SP and more than 1000 Million vests.